The garment industry has experienced rapid technological expansion due to scientific developments in laminating and coating techniques. Originally, polymers such as thermoset and thermoplastic polyurethane, silicon rubber, polyvinylchloride, and the like were used to coat and produce waterproof fabrics used in the manufacture of rainwear. Unfortunately, these garments suffered from several drawbacks, and consumers found the garments uncomfortable. Although polymer coatings did not let liquid water in, the coated fabrics did not permit satisfactory evaporation of the users' perspiration, thus causing discomfort and chilling.
It is now known that a waterproof garment can be rendered breathable by providing the fabric with a microporous layer. This layer allows for passage of water vapor by diffusion from inside the garment, through the microporous structure, to the outside due to the vapor pressure gradient across the microporous layer. The small size of the surface micropores, on the order of 1.0 micron, and the high surface tension of liquid water, combine to prohibit the passage of liquid water through the membrane. A number of products for use in sports, outerwear and camping have been manufactured by laminating membranes with these properties to shell fabrics. One such garment is described in U.S. Pat. No. 4,194,041 to Gore et al.
Several drawbacks exist in the practice of the above disclosed invention. The microporous layer is composed of polytetrafluoroethylene (PTFE) which has no known practical solvent. The manufacturing technique used to produce the membrane is therefore rigid and costly. To be rendered useful, an extruded film of the PTFE must be heated to its crystalline melt point under controlled tension, thus producing a microporous PTFE membrane. An additional lamination step for adhesion of the PTFE membrane to the garment fabric is also required.
Microporous membranes have also been used for microfiltration and reverse osmosis. These microporous membranes are normally prepared by treating a solvent solution of a suitable polymer with a liquid that is miscible with the solvent and acts as a non-solvent for the polymer. The process is commonly referred to as the solvent/non-solvent method. Variations of this method are described in U.S. Pat. Nos. 4,203,848, 4,316,722 and 4,384,047. In the above applications the objective is to prepare a microporous membrane of a specific pore size and very small pore size distribution.
However, a number of problems must be overcome in order to use this technique on textile substrates. Filtration membranes produced using the solvent/non-solvent process usually possess a high flexural modulus. Filtration membranes manufactured from thermoplastic polyvinylidene fluoride (PVDF) for example, exhibit a bending radius well above 3.0 centimeters when subjected to stiffness testing as provided in ASTM D1388-64. A fabric attached to the above filtration membranes would possess undesirable stiffness due to the high membrane bending radius.
Further, the microporous membranes used in filtration technology are prepared from fully reacted polymers and do not possess adhesion properties. Additionally, application of the liquid polymer solutions used to produce filtration membranes to the surface of the textile fabrics results in polymer solution striking through the fabric. The polymer fills the space between the normally freely moving fibers. This adversely affects the breathability and hand, or feel, of the fabric, making it overly stiff.
U.S. Pat. No. 3,748,217 describes the use of foamed polymeric materials in the manufacture of draperies. The foamed materials are used as backing material, and in conjunction with bonded non-woven materials to modify the appearance and drape of the textile fabrics, and to increase opacity of the product.
Two basic techniques are used for the production of foamed materials. One involves the reaction of prepolymers with the production of a gas as a side product. The produced gas acts as a blowing agent for the reacting polymer, producing the foam structure. This technique involves the use of toxic and difficult to handle materials such as isocyanates. The second technique involves the addition of precisely metered amounts of an inert gas into a water or solvent-based solution of a fully reacted polymer. These mechanically produced foams have also been used for bonding paper and non-woven fabrics. In the above applications, the problems of substrate breathability, adhesive strike-through and stiffness of feel are not addressed.
A fabric coated with a suitable microporous membrane may have acceptable breathability and waterproofness. However no garment could be made from this coated fabric since the microporous membrane is very delicate and susceptible to damage during manufacture and use of the garment. It is very difficult to attach a protective layer to a fully reacted, highly crosslinked polymer such as PTFE or PVDF from which a microporous membrane has been prepared. To overcome this problem, U.S. Pat. No. 4,194,041 uses costly laminating techniques and reactive, toxic and difficult to handle pre-polymers.